For some version (maybe all of them) there was (is?) a bug that the addon reference in the mission.sqm was (is?) not updated if you have inserted an object requiring an addon and then removed it in the editor.
Was that diplomatic enough?
In eathly terms:
I have an empty map and I place a BAS ranger soldier and save the mission.
--> OFP writes in the mission.sqm that this addon is used.
I remove the BAS ranger soldier and save the mission.
--> OFP removes the soldier from the mission.sqm but not the addon
from the reference in mission.sqm.
Result:
I have an empty map, that needs the Delta/Ranger pack in order to work.
Fix:
Manually remove the the addon reference from the mission.sqm.